1. Field of Invention
The present invention relates to an actuator. More particularly, the present invention relates to an actuator applicable to lens modules.
2. Description of Related Art
Various high-tech products have been developed with the popularity of modern science and technology and the improvement of the living standard, among which the most representative ones are digital information products, such as mobile phones and digital cameras. In recent years, as digital cameras are integrated into mobile phones, camera phones have become the dominant products in the mobile phone market, and various camera phones are available in the market. With the increase of the added value of products and driven by the consumption models of consumers, cameras in mobile phones are developing toward the trend of high image quality, low power consumption, low cost and miniaturization, and actuators in lens modules of the cameras are key components influencing the overall quality.
Currently, actuators applied in miniature lens modules are roughly classified into two categories according to the moving modes of the actuators. The actuators in the first category provide rotary power to drive the lens modules, and the direction of the rotating axis is parallel to the optical axis. The actuators in the second category provide translational power to drive the lens modules, and the direction of translation is parallel to the optical axis.
More particularly, the actuators of the first category need additional mechanisms which convert transmission direction to enable the lens modules to move parallel to the optical axis. The advantage of the actuators is that no additional power is needed to lo maintain the specific position after the position is reached. However, the structure of the actuators has many components, and is complicated, which is disadvantageous for the reduction of the size and cost. Common actuators of this category include step motors. As described above, because being disadvantageous for the reduction of size and cost, the kind of actuators are gradually losing their market share.
In addition, the actuators of the second category provide power parallel to the moving direction, so additional mechanisms which convert transmission direction are not required. Compared to the actuators of the first category, they may effectively reduce the number of components and the size. Common actuators of this category include voice coil actuators, piezoelectric actuators, and liquid lenses, etc. The piezoelectric actuators require high manufacturing cost and power consumption, and are disadvantageous in market competition and popularization. Similarly, the liquid lenses have to be driven with high voltage sources, and are disadvantageous in market competition and popularization as well. Compared to the two types of actuators described above, the voice coil actuators have lower manufacturing cost and high positioning precision, and are advantageous in the market. However, if the voice coil actuators are to be maintained at the specific position after they are positioned, continuous power supply and repetitive control are required, that lead to the waste of power and the reduction of the battery life of portable devices. Moreover, the voice coil actuators have low anti-shock performance, and are disadvantageous in long-time positioning.
To make actuators in lens modules more suitable for portable devices (such as camera phones), the trend now is miniaturization, low power consumption, and low cost. As shown in FIG. 1, U.S. Pat. No. 6,856,469 discloses a lens driving device 100, which is characterized in that a magnetic element 110, a flexible element 120 and a spring element 130 are arranged in a direction parallel to the optical axis, and the clamping action for positioning is performed by using the magnetic force of the magnetic element 110 and a magnet 140 together with the spring element 130. However, as the displacement of the magnetic element 110 generated with the change of the magnetic force is nonlinear, it is difficult to control the positioning. Furthermore, as the magnetic force between the magnetic element 110 and the magnet 140 is great, a high current is required to balance the magnetic force, which is also disadvantageous for the miniaturization of the device.
In addition, as shown in FIG. 2A and FIG. 2B, European Patent No. 2005/060242A1 discloses a camera apparatus, which is characterized in that a magnetic element 210, a coil 220, a rotating axis 230 and an elastic element form a clamping mechanism 200, and the magnetic attraction force between the magnetic element 210 and the coil 220 and the restoring force of the elastic element are used to enable the clamping element 240 to release or clamp a focus driving part 250 at specific positions. However, as the apparatus has a large number of elements and a complicated structure, it is difficult to assemble, and is disadvantageous in the miniaturization of the device.
FIG. 3 is an actuator 300 disclosed in Japanese Patent No. 2005-128405, which is characterized in that a spring plate 310 and a spring plate 320 specially designed to be arranged vertically are used to provide precise movement of the lens module and reduce the friction during the movement, and the spring plates may be regarded as the extension of a coil, and serve as the conductor for the flow of the current in two ends of the coil. Moreover, a groove 340 in an outer frame 330 and a flange 360 on a lens module 350 bear the collision or vibration caused by the contact of a moving body and a fixed body, thereby controlling the deviation of the moving body to the optical axis within an acceptable range, so as to prevent the over rotation of the moving body from influencing other structures.
Furthermore, it should be noted that the actuator structures of the conventional technologies described above all use radially magnetized permanent magnets (i.e., permanent magnets having radial magnetic polarity direction). For example, Japanese Patent No. 2005-128405 shown in FIG. 3 uses a plurality of radially magnetized permanent magnets 370 and U-shaped yoke 380. However, the current mass production technology of permanent magnets cannot radially magnetize a permanent magnet with an enclosed shape to a single polarity, so the permanent magnet with an enclosed shape has to be cut into several blocks, which will be then radially magnetized individually. Thus, the manufacturing cost and the difficulty in assembling is increased, and the availability of the magnetic energy product is poor. In addition, in order to improve the availability of the magnetic energy product, the section of the yoke has to be designed to a U-shape, so the manufacturing cost of the yoke is high. Conventional actuator structures using radially magnetized permanent magnets are difficult to manufacture and assemble, and are disadvantageous in the reduction of cost.